Research on performance of CFST column to steel beam joint with through bolts-extended endplate against progressive collapse

In order to investigate the performance of the concrete filled steel tubular (CFST) column to steel beam joint with through bolts-extended endplate against progressive collapse, a monotonic loading test was conducted. The deformation process, failure modes, column resistance, and key section strains were observed and analyzed. The finite element model of these joints was established to study the fracture behavior, stress development and resistance mechanism of the joint. The results show that the CFST column-steel beam joint with through bolts-extended endplate undergoes four stages to reach progressive collapse, i.e., beam mechanism stage, mixing mechanism stage, catenary mechanism stage and failure stage. The resistance of the joint against progressive collapse is provided by the bending capacity and the tensile capacity. The tensile capacity contributes more resistance to the joint against progressive collapse than the bending capacity. The collapse fracture of the joint generally occurs at the connection-section of the extended endplate and the steel beam. After the crack penetrates the lower flange, it quickly extends to the web of the beam. The tensile stress of the through bolts below the centroidal axis continues to increase. The tensile stress of the through bolts above the centroidal axis is small at the initial stage of loading, and gradually increases with the increase of vertical displacement. For extended endplate, the stress mainly concentrates around the bolt hole. With the increasing of the vertical displacement, the stress concentration area above the centroidal axis decreases, and the stress below the centroidal axis increases. © 2019, Editorial Office of Journal of Building Structures. All right reserved.